Thanks to big shifts in several key races, Democrats now have a 73 percent chance of winning the Senate, according to the FiveThirtyEight polls-plus forecast, and a 72 percent chance according to polls-only. Both those numbers are up by more than 15 percentage points from last week, when the polls-plus model gave them a 56 percent chance and the polls-only model 54 percent.In our last Senate Update, I noted a growing divergence between our Senate and presidential forecasts.